1. Field of the Invention
The present invention relates to an image forming apparatus that includes a consumable part such as a cartridge having a storage unit like a nonvolatile memory, and a control method of the image forming apparatus.
2. Description of the Related Art
Conventionally, in copying machines or laser beam printers that use electrophotographic technologies, various components used for image formation are integrally formed as a cartridge. Such a cartridge is consumable, and is replaced when it reaches the end of its lifetime.
Some of such cartridges have a built-in nonvolatile memory (for example, an electrically erasable programmable read-only memory (EEPROM)). The cartridge having a built-in memory stores information about a lifetime of the cartridge, for example, cumulative length of the rotation time of a photosensitive drum which is a component of the cartridge, and a remaining amount of toner. A printer control unit reads the stored information about the lifetime of the cartridge, determines the consumed amount of the cartridge, and changes print conditions or the like.
Japanese Patent Application Laid-Open No. 2001-312110 proposes a method for storing in a memory the number of times of image formation that has been accumulated. Based on the accumulated number of times of image formation, transfer bias is changed to form an image of stable quality. Japanese Patent Application Laid-Open No. 05-027502 proposes a method for determining a lifetime of a process cartridge. In a case where the process cartridge is used so long that the print quality cannot be maintained anymore, the life-end information is stored in the memory, and a user is notified that the process cartridge has reached the end of its life.
Not only the cartridges, but also the memories such as the EEPROM have their lifetime. That is, these memories have upper limits in the number of times of rewrite. The upper limits are generally called the guaranteed number of times of rewrite. Meanwhile, in recent years, as processing speeds of the image forming apparatuses are enhanced, capacities of the process cartridges are largely increased, and the number of times of rewrite of the memories is also being increased. To cope with the increase of the number of times of rewrite, for example, a higher-performance memory that can be more frequently rewritten can be employed. However, in this way, the memory cost increases. Furthermore, as the memory cost increases, a cost of the cartridge which is a consumable part also increases.
If the number of times of rewrite can be reduced, the above-described problems can be solved. For example, if data can be rewritten in a lump for certain volume of the print sheets, the number of times of memory rewrite can be reduced. However, if a power of an apparatus is turned off before the rewrite of the memory is completed, the data rewrite cannot be executed, and the accuracy (reliability) of the data may be lowered.
Further, the memory is mounted on the cartridge and replaced together with the cartridge. When the lifetime of the cartridge ends, the memory may be still usable. That is a wasteful way from the viewpoint of costs. Thus, if it is possible to make the end of the lifetime of the cartridge close to the end of the lifetime of the memory as much as possible, the memory can be effectively used.